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Frontiers in Pharmacology 2023Alzheimer's disease (AD), one of the most prevalent neurodegenerative diseases is associated with pathological autophagy-lysosomal pathway dysfunction. Dexmedetomidine...
Alzheimer's disease (AD), one of the most prevalent neurodegenerative diseases is associated with pathological autophagy-lysosomal pathway dysfunction. Dexmedetomidine (Dex) has been suggested as an adjuvant to general anesthesia with advantages in reducing the incidence of postoperative cognitive dysfunction in Dex-treated patients with AD and older individuals. Several studies reported that Dex improved memory; however, evidence on the effects of Dex on neuronal autophagy dysfunction in the AD model is lacking. We hypothesized that Dex administration would have neuroprotective effects by improving pathological autophagy dysfunction in mice that received an intracerebroventricular (i.c.v.) injection of amyloid β-protein fragment 25-35 (Aβ) and in an autophagy-deficient cellular model. In the Y-maze test, Dex reversed the decreased activity of Aβ mice. Additionally, it restored the levels of two memory-related proteins, phosphorylated Ca/calmodulin-dependent protein kinase II (p-CaMKII) and postsynaptic density-95 (PSD-95) in Aβ mice and organotypic hippocampal slice culture (OHSC) with Aβ. Dex administration also resulted in decreased expression of the autophagy-related microtubule-associated proteins light chain 3-II (LC3-II), p62, lysosome-associated membrane protein2 (LAMP2), and cathepsin D in Aβ mice and OHSC with Aβ. Increased numbers of co-localized puncta of LC3-LAMP2 or LC3-cathepsin D, along with dissociated LC3-p62 immunoreactivity following Dex treatment, were observed. These findings were consistent with the results of western blots and the transformation of double-membrane autophagosomes into single-membraned autolysosomes in ultrastructures. It was evident that Dex treatment alleviated impaired autolysosome formation in Aβ mice. Our study demonstrated the improvement of memory impairment caused by Dex and its neuroprotective mechanism by investigating the role of the autophagy-lysosomal pathway in a murine Aβ model. These findings suggest that Dex could be used as a potential neuroprotective adjuvant in general anesthesia to prevent cognitive decline.
PubMed: 37663257
DOI: 10.3389/fphar.2023.1184776 -
Philosophical Transactions of the Royal... Jul 2024Which proportion of the long-term potentiation (LTP) expressed in the bulk of excitatory synapses is postsynaptic and which presynaptic remains debatable. To understand...
Which proportion of the long-term potentiation (LTP) expressed in the bulk of excitatory synapses is postsynaptic and which presynaptic remains debatable. To understand better the possible impact of either LTP form, we explored a realistic model of a CA1 pyramidal cell equipped with known membrane mechanisms and multiple, stochastic excitatory axo-spinous synapses. Our simulations were designed to establish an input-output transfer function, the dependence between the frequency of presynaptic action potentials triggering probabilistic synaptic discharges and the average frequency of postsynaptic spiking. We found that, within the typical physiological range, potentiation of the postsynaptic current results in a greater overall output than an equivalent increase in presynaptic release probability. This difference grows stronger at lower input frequencies and lower release probabilities. Simulations with a non-hierarchical circular network of principal neurons indicated that equal increases in either synaptic fidelity or synaptic strength of individual connections also produce distinct changes in network activity, although the network phenomenology is likely to be complex. These observations should help to interpret the machinery of LTP phenomena documented . This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.
Topics: Long-Term Potentiation; Models, Neurological; Synapses; Pyramidal Cells; Animals; Computer Simulation; Action Potentials; CA1 Region, Hippocampal
PubMed: 38853561
DOI: 10.1098/rstb.2023.0235 -
Neuropathology and Applied Neurobiology Aug 2023Synaptic strength depends strongly on the subsynaptic organisation of presynaptic transmitter release and postsynaptic receptor densities, and their alterations are...
AIMS
Synaptic strength depends strongly on the subsynaptic organisation of presynaptic transmitter release and postsynaptic receptor densities, and their alterations are expected to underlie pathologies. Although synaptic dysfunctions are common pathogenic traits of Alzheimer's disease (AD), it remains unknown whether synaptic protein nano-organisation is altered in AD. Here, we systematically characterised the alterations in the subsynaptic organisation in cellular and mouse models of AD.
METHODS
We used immunostaining and super-resolution stochastic optical reconstruction microscopy imaging to quantitatively examine the synaptic protein nano-organisation in both Aβ1-42-treated neuronal cultures and cortical sections from a mouse model of AD, APP23 mice.
RESULTS
We found that Aβ1-42-treatment of cultured hippocampal neurons decreased the synaptic retention of postsynaptic scaffolds and receptors and disrupted their nanoscale alignment to presynaptic transmitter release sites. In cortical sections, we found that while GluA1 receptors in wild-type mice were organised in subsynaptic nanoclusters with high local densities, receptors in APP23 mice distributed more homogeneously within synapses. This reorganisation, together with the reduced overall receptor density, led to reduced glutamatergic synaptic transmission. Meanwhile, the transsynaptic alignment between presynaptic release-guiding RIM1/2 and postsynaptic scaffolding protein PSD-95 was reduced in APP23 mice. Importantly, these reorganisations were progressive with age and were more pronounced in synapses in close vicinity of Aβ plaques with dense cores.
CONCLUSIONS
Our study revealed a spatiotemporal-specific reorganisation of synaptic nanostructures in AD and identifies dense-core amyloid plaques as the major local inductor in APP23 mice.
Topics: Mice; Animals; Alzheimer Disease; Synapses; Neurons; Synaptic Transmission; Amyloid beta-Peptides; Disease Models, Animal; Mice, Transgenic
PubMed: 37461203
DOI: 10.1111/nan.12924 -
The Journal of Neuroscience : the... Jul 2023During the first two postnatal weeks, intraneuronal chloride concentrations in rodents gradually decrease, causing a shift from depolarizing to hyperpolarizing GABA...
During the first two postnatal weeks, intraneuronal chloride concentrations in rodents gradually decrease, causing a shift from depolarizing to hyperpolarizing GABA responses. The postnatal GABA shift is delayed in rodent models for neurodevelopmental disorders and in human patients, but the impact of a delayed GABA shift on the developing brain remains obscure. Here we examine the direct and indirect consequences of a delayed postnatal GABA shift on network development in organotypic hippocampal cultures made from 6- to 7-d-old mice by treating the cultures for 1 week with VU0463271, a specific inhibitor of the chloride exporter KCC2. We verified that VU treatment delayed the GABA shift and kept GABA signaling depolarizing until DIV9. We found that the structural and functional development of excitatory and inhibitory synapses at DIV9 was not affected after VU treatment. In line with previous studies, we observed that GABA signaling was already inhibitory in control and VU-treated postnatal slices. Surprisingly, 14 d after the VU treatment had ended (DIV21), we observed an increased frequency of spontaneous inhibitory postsynaptic currents in CA1 pyramidal cells, while excitatory currents were not changed. Synapse numbers and release probability were unaffected. We found that dendrite-targeting interneurons in the stratum radiatum had an elevated resting membrane potential, while pyramidal cells were less excitable compared with control slices. Our results show that depolarizing GABA signaling does not promote synapse formation after P7, and suggest that postnatal intracellular chloride levels indirectly affect membrane properties in a cell-specific manner. During brain development, the action of neurotransmitter GABA shifts from depolarizing to hyperpolarizing. This shift is a thought to play a critical role in synapse formation. A delayed shift is common in rodent models for neurodevelopmental disorders and in human patients, but its consequences for synaptic development remain obscure. Here, we delayed the GABA shift by 1 week in organotypic hippocampal cultures and carefully examined the consequences for circuit development. We find that delaying the shift has no direct effects on synaptic development, but instead leads to indirect, cell type-specific changes in membrane properties. Our data call for careful assessment of alterations in cellular excitability in neurodevelopmental disorders.
Topics: Animals; Mice; Humans; Chlorides; Hippocampus; Interneurons; Synapses; gamma-Aminobutyric Acid; Synaptic Transmission
PubMed: 37438107
DOI: 10.1523/JNEUROSCI.0251-23.2023 -
Journal of Psychiatric Research Jul 2023Posttraumatic stress disorder (PTSD), a psychiatric disorder caused by stressful events, is characterized by long-lasting fear memory. The nucleus accumbens shell (NAcS)...
BACKGROUND
Posttraumatic stress disorder (PTSD), a psychiatric disorder caused by stressful events, is characterized by long-lasting fear memory. The nucleus accumbens shell (NAcS) is a key brain region that regulates fear-associated behavior. Small-conductance calcium-activated potassium channels (SK channels) play a key role in regulating the excitability of NAcS medium spiny neurons (MSNs) but their mechanisms of action in fear freezing are unclear.
METHOD
We established an animal model of traumatic memory using conditioned fear freezing paradigm, and investigated the alterations in SK channels of NAc MSNs subsequent to fear conditioning in mice. We then utilized an adeno-associated virus (AAV) transfection system to overexpress the SK3 subunit and explore the function of the NAcS MSNs SK3 channel in conditioned fear freezing.
RESULTS
Fear conditioning activated NAcS MSNs with enhanced excitability and reduced the SK channel-mediated medium after-hyperpolarization (mAHP) amplitude. The expression of NAcS SK3 were also reduced time-dependently. The overexpression of NAcS SK3 impaired conditioned fear consolidation without affecting conditioned fear expression, and blocked fear conditioning-induced alterations in NAcS MSNs excitability and mAHP amplitude. Additionally, the amplitudes of mEPSC, AMPAR/NMDAR ratio, and membrane surface GluA1/A2 expression in NAcS MSNs was increased by fear conditioning and returned to normal levels upon SK3 overexpression, indicating that fear conditioning-induced decrease of SK3 expression caused postsynaptic excitation by facilitating AMPAR transmission to the membrane.
CONCLUSION
These findings show that the NAcS MSNs SK3 channel plays a critical role in conditioned fear consolidation and that it may influence PTSD pathogenesis, making it a potential therapeutic target against PTSD.
Topics: Mice; Animals; Small-Conductance Calcium-Activated Potassium Channels; Nucleus Accumbens; Freezing; Fear; Phobic Disorders
PubMed: 37216772
DOI: 10.1016/j.jpsychires.2023.05.057 -
Molecular Cell Jan 2024Membraneless organelles formed by phase separation of proteins and nucleic acids play diverse cellular functions. Whether and, if yes, how membraneless organelles in...
Membraneless organelles formed by phase separation of proteins and nucleic acids play diverse cellular functions. Whether and, if yes, how membraneless organelles in ways analogous to membrane-based organelles also undergo regulated fusion and fission is unknown. Here, using a partially reconstituted mammalian postsynaptic density (PSD) condensate as a paradigm, we show that membraneless organelles can undergo phosphorylation-dependent fusion and fission. Without phosphorylation of the SAPAP guanylate kinase domain-binding repeats, the upper and lower layers of PSD protein mixtures form two immiscible sub-compartments in a phase-in-phase organization. Phosphorylation of SAPAP leads to fusion of the two sub-compartments into one condensate accompanied with an increased Stargazin density in the condensate. Dephosphorylation of SAPAP can reverse this event. Preventing SAPAP phosphorylation in vivo leads to increased separation of proteins from the lower and upper layers of PSD sub-compartments. Thus, analogous to membrane-based organelles, membraneless organelles can also undergo regulated fusion and fission.
Topics: Animals; Biomolecular Condensates; Phosphorylation; Post-Synaptic Density; Cell Physiological Phenomena; Protein Binding; Organelles; Mammals
PubMed: 38096828
DOI: 10.1016/j.molcel.2023.11.011 -
International Immunopharmacology Dec 2023Currently, there are no effective therapeutic targets for the treatment of chronic cerebral hypoperfusion(CCH)-induced cerebral ischemic injury. Vascular endothelial...
Currently, there are no effective therapeutic targets for the treatment of chronic cerebral hypoperfusion(CCH)-induced cerebral ischemic injury. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are discovered as the inducers of neurogenesis and angiogenesis. We previously made a nanofiber membrane (NFM), maintaining a long-term release of VEGF and bFGF up to 35 days, which might make VEGF and bFGF NFM as the potential protective agents against cerebral ischemic insult. In this study, the effects of VEGF and bFGF delivered by NFM into brain were investigated as well as their underlying mechanismsin a rat model of CCH. VEGF + bFGF NFM application increased the expressions of tight junction proteins, maintained BBB integrity, and alleviated vasogenic cerebral edema. Furthermore, VEGF + bFGF NFM sticking enhanced angiogenesis and elevated CBF. Besides, VEGF + bFGF NFM treatment inhibited neuronal apoptosis and decreased neuronal loss. Moreover, roofing of VEGF + bFGF NFM attenuated microglial activation and blocked the launch of NLRP3/caspase-1/IL-1β pathway. In addition, VEGF + bFGF NFM administration prevented disruption to the pre/postsynaptic membranes and loss of myelin sheath, relieving synaptic injury and demyelination. Oligodendrogenesis, neurogenesis and PI3K/AKT/mTOR pathway were involved in the treatment of VEGF + bFGF NFM against CCH-induced neuronal injury and hypomyelination. These findings supported that VEGF + bFGF NFM application constitutes a neuroprotective strategy for the treatment of CCH, which may be worth further clinical translational research as a novel neuroprotective approach, benifiting indirect surgical revascularization.
Topics: Rats; Animals; Vascular Endothelial Growth Factor A; Fibroblast Growth Factor 2; Phosphatidylinositol 3-Kinases; Nanofibers; Vascular Endothelial Growth Factors; Brain Ischemia; Ischemia; Brain Injuries
PubMed: 37890380
DOI: 10.1016/j.intimp.2023.111108 -
Endocrinology Sep 2023It is well-established that the hypothalamic-pituitary-gonadal (HPG) axis is suppressed due to negative energy balance. However, less information is available on whether...
It is well-established that the hypothalamic-pituitary-gonadal (HPG) axis is suppressed due to negative energy balance. However, less information is available on whether kisspeptin neuronal activity contributes to fasting-induced responses. In the present study, female and male mice were fasted for 24 hours or provided food ad libitum (fed group) to determine whether acute fasting is sufficient to modulate kisspeptin neuronal activity. In female mice, fasting attenuated luteinizing hormone (LH) and prolactin (PRL) serum levels and increased follicle-stimulating hormone levels compared with the fed group. In contrast, fasting did not affect gonadotropin or PRL secretion in male mice. By measuring genes related to LH pulse generation in micropunches obtained from the arcuate nucleus of the hypothalamus (ARH), we observed that fasting reduced Kiss1 mRNA levels in female and male mice. In contrast, Pdyn expression was upregulated only in fasted female mice, whereas no changes in the Tac2 mRNA levels were observed in both sexes. Interestingly, the frequency and amplitude of the GABAergic postsynaptic currents recorded from ARH kisspeptin neurons (ARHKisspeptin) were reduced in 24-hour fasted female mice but not in males. Additionally, neuropeptide Y induced a hyperpolarization in the resting membrane potential of ARHKisspeptin neurons of fed female mice but not in males. Thus, the response of ARHKisspeptin neurons to fasting is sexually dependent with a female bias, associated with changes in gonadotropins and PRL secretion. Our findings suggest that GABAergic transmission to ARHKisspeptin neurons modulates the activity of the HPG axis during situations of negative energy balance.
Topics: Mice; Female; Male; Animals; Kisspeptins; Luteinizing Hormone; Synaptic Transmission; Neurons; Arcuate Nucleus of Hypothalamus; Fasting; RNA, Messenger
PubMed: 37793082
DOI: 10.1210/endocr/bqad150 -
Experimental Gerontology Nov 2023Sarcopenia involves in the loss of muscle mass associated with aging, which is the major cause of progressive muscle weakness and deterioration in older adults. Muscle...
Sarcopenia involves in the loss of muscle mass associated with aging, which is the major cause of progressive muscle weakness and deterioration in older adults. Muscle atrophy is a direct presentation of sarcopenia, and it greatly contributes to the decline in quality of life among older adults. Neuromuscular junction (NMJ) stability is the key link to maintain muscle function. Besides, the degenerative change of NMJ promotes the process of muscle atrophy in the elderly. Based on previous transcriptome sequencing and bioinformatics analyses of aged muscle, this study used the 18-month-old aged mouse model and the 6-month-old young mouse model to deliberate the role and underlying mechanisms of Cullin-3 (Cul3) in age-related muscle atrophy. The results of reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblotting analysis showed that the expression of CUL3 increased in aged muscle tissue, while the expression level of postsynaptic membrane nicotinic acetylcholine receptors (nAChRs) decreased significantly, which manfested a negative correlation. Meanwhile, immunofluorescence demonstrated that Cul3 was highly expressed in senile muscle NMJ. The results of ubiquitin indicated that the ubiquitin level of aged muscle nAChRs was evidently increased. Co-immunoprecipitation furtherly verified the correlation between Cul3 and nAChRs. Taken together, Cul3 may mediate the ubiquitination degradation of nAChRs protein at the NMJ site in aged mice, leading to NMJ degeneration and accelerated atrophy of fast-twitch muscle fibers in aged muscle. As a prominent element to maintain the stability of NMJ, Cul3 is supposed to be one of candidate intervention targets in sarcopenia.
Topics: Animals; Mice; Cullin Proteins; Muscle, Skeletal; Muscular Atrophy; Neuromuscular Junction; Quality of Life; Receptors, Nicotinic; Sarcopenia; Ubiquitination; Ubiquitins
PubMed: 37913946
DOI: 10.1016/j.exger.2023.112318 -
Frontiers in Molecular Neuroscience 2023Postsynaptic neurotransmitter receptors and their associated scaffolding proteins assemble into discrete, nanometer-scale subsynaptic domains (SSDs) within the...
Postsynaptic neurotransmitter receptors and their associated scaffolding proteins assemble into discrete, nanometer-scale subsynaptic domains (SSDs) within the postsynaptic membrane at both excitatory and inhibitory synapses. Intriguingly, postsynaptic receptor SSDs are mirrored by closely apposed presynaptic active zones. These trans-synaptic molecular assemblies are thought to be important for efficient neurotransmission because they concentrate postsynaptic receptors near sites of presynaptic neurotransmitter release. While previous studies have characterized the role of synaptic activity in sculpting the number, size, and distribution of postsynaptic SSDs at established synapses, it remains unknown whether neurotransmitter signaling is required for their initial assembly during synapse development. Here, we evaluated synaptic nano-architecture under conditions where presynaptic neurotransmitter release was blocked prior to, and throughout synaptogenesis with tetanus neurotoxin (TeNT). In agreement with previous work, neurotransmitter release was not required for the formation of excitatory or inhibitory synapses. The overall size of the postsynaptic specialization at both excitatory and inhibitory synapses was reduced at chronically silenced synapses. However, both AMPARs and GABARs still coalesced into SSDs, along with their respective scaffold proteins. Presynaptic active zone assemblies, defined by RIM1, were smaller and more numerous at silenced synapses, but maintained alignment with postsynaptic AMPAR SSDs. Thus, basic features of synaptic nano-architecture, including assembly of receptors and scaffolds into trans-synaptically aligned structures, are intrinsic properties that can be further regulated by subsequent activity-dependent mechanisms.
PubMed: 37602191
DOI: 10.3389/fnmol.2023.1232795